The pyroantimonate method for the ultrastructural localization of calcium has been applied to the retina pigment epithelium. With simultaneous osmium fixation at pH 9.2 calcium antimonate precipitate has been demonstrated in the extracellular space of the choroid, along Bruch's membrane, in the mitochondria and nucleus of the RPE, and within the discs of the rod outer segments. The identification of the precipitate as calcium antimonate has been accomplished by the use of the electron microprobe. This technique has implications for the identification and quantitation of calcium in ocular tissues, as well as changes produced by physiologic or pathologic processes.